This invention relates to a method and apparatus for testing an electric motor to determine over a short testing interval whether the motor is operative.
During final production testing of an electric motor, visual inspection of rotation of the motor may be possible or difficult for a variety of reasons. For example, rotation of an output shaft of a timing motor which drives a step-down gear train may be imperceptible over a short time period during which testing should be accomplished. Similarly, the motor may be part of an enclosed assembly which does not allow for any visual inspection of moving parts. It would be desirable to provide a testing method and apparatus which can determine, in an extremely short time interval, whether an electric motor is operative or inoperative. To maintain a high rate of production, the method must be simple and desirably should require no connection to the output shaft
It has been known to utilize the residual magnetic field of an electric motor to operate an indicator to indicate that an appliance has completed a cycle. An example of such a device is disclosed in U.S. Pat. No. 3,004,205 issued Oct. 10, 1961 to Barritt and Fuqua, and assigned to the assignee of the present application. In the Barritt et al patent, the end of the cycle of an automatic clothes dryer is signaled by an audible indication which is generated in response to the momentary transient voltage induced in the winding of an electric motor by residual decaying circulating rotor currents existing in the rotating rotor immediately following de-energization of the motor.